This invention relates to induction furnaces and, in particular, to a continuous flow induction furnace for use in melting high temperature materials such as glasses, refractories, ceramics, or the like and utilizes graphite susceptors which permits ready replacement thereof.
The prior art abounds with electric furnaces for the production of silicon and other materials of similar nature. Often, these furnaces also utilize induction heating in order to reduce the raw material to a molten mass. However, few of these furnaces are of the continuous flow type.
United States patents to Schneider et al on Jan. 18, 1972 having U.S. Pat. No. 3,636,293; Beckius et al on May 21, 1957 having U.S. Pat. No. 2,793,242; and Conant on Dec. 11, 1956 having U.S. Pat. No. 2,773,750 appear to be the most pertinent.
The patent to Schneider et al discloses a continuous flow furnace utilized for melting vitreous-type materials by means of induction heating. The materials to be melted are supported in an electrically conductive cylindrically-shaped susceptor and are temporarily supported on a refractory support mounted within the cylinder. The refractory support is provided with a plurality of orifices through which the materials, melted by heat radiated from the inductively heated susceptor, may flow into a lower chamber. The material in the lower chamber is held with additional heating for a time sufficient to complete the required time-temperature relationship. The susceptor cylinder is divided into sections and may be fabricated of graphite while the refractory supports may be fabricated of zircon or graphite.
The patent to Beckius et al, relates to the production of silicon and other similar materials, and discloses a continuous flow electrical induction furnace, including a plurality of heating zones and a multi-sectioned graphite cylinder susceptor serving as a secondary winding for generating heat provided for the charged material. The susceptor cylinder sections are mounted one above the other in interlocking manner and are surrounded by a pulverulent easily removable layer of heat resistant material which permits the ready replacement of susceptor sections as they are consumed in the melting process.
The patent to Conant relates to a continuous flow furnace utilized for the heat treatment of materials which are accompanied by the presence of gases or vapors and includes means to effect the separation of the solid, vapor and molten states of the charged material, providing separate discharge paths for the vapor and molten states thereof. The furnace utilizes induction heating with a cylindrically-shaped susceptor which may be fabricated of graphite and includes a conically-shaped core with a recessed opening on the bottom thereof, adapted to receive a weir which is threaded into the bottom portion of the furnace and is provided with an aperture communicating with the outside thereof. The furnace is a small scale device which utilizes high frequencies for operation and is of low efficiency. As discussed above, prior art does not disclose the configuration of the present invention or is there any suggestion thereof. The features disclosed in the present invention which include a plurality of susceptor sections stacked one upon the other to form a cylinder with selected sections including a conically shaped baffle surrounded by a plurality of orifices for the molten charge to flow therethrough and be directed to provide a mixing thereof, has not been shown or suggested. The specific construction of the present furnace with regard to the susceptor, insulator and reactor shield relationship with respect to a tapped induction coil has not been shown or suggested.
The instant invention overcomes the shortcomings found in the prior art by providing a continuous stream of molten material with the capability of closely and independently controlling both the flow rate and the temperature of the molten stream. The furnace is a closed system involving no gaseous effluents, and hence there are no pollution control requirements. The same furnace construction may be used for a wide variety of materials and a wide range of melt rates and tap temperatures can be achieved with ease. The present furnace has very low maintenance requirements, long campaign life, low consumable costs, and is capable of starting and stopping in a small fraction of the time required by other furnaces currently known in the state of the art.
Therefore, it is the object of the present invention to provide a relatively inexpensive continuous flow induction furnace for the pollution free melting of high temperature non-conducting (non-metallic) materials such as glasses, refractories, ceramics or the like.
Another object of the present invention is to provide a continuous flow induction furnace which utilizes a susceptor which is also the container vehicle.
A further object of the present invention is to provide an induction furnace which includes specially designed baffle configurations disposed within the susceptor to maximize the transfer of heat into the charge.
A still further object of the present invention is to provide an induction furnace having graphite hearths which permits continuous tapping of the furnace without permitting solid (unmelted) materials to be entrained in the melt stream.
Another object of the present invention is to provide an induction furnace which utilizes a tapped induction coil disposed along the longitudinal axis of the furnace enabling proper distribution of the power input over the length or height of the susceptor so that the melt rate and tap temperature may be varied independently and in a controlled fashion.
Still another object of the present invention is to provide an induction furnace which includes means for easy replacement of the susceptor element.
Yet another object of the present invention is to provide an induction furnace which utilizes a fully charged, continuously loaded, closed system at all times, so that the graphite susceptor and hearth are effectively protected against air oxidation and has literally no gaseous effluent.
An additional object of the present invention is to provide a graphite susceptor for the efficient use of low frequency electrical energy for heating.
Still an additional object of the present invention is to provide a graphite susceptor which resists attack by molten oxide materials.